Help a SS noob choose: 42-17 or 42-18?

Building up my first SS which has a 42 tooth chainring. Trying to decide between a 17 or 18 cog. I live in Southern NH, always mildly hilly. I'm 135# and a good climber. Like to spin relatively high cadences.

Used a gear inch calculator; for my setup, 42-17 is 68.2 inches and 42-18 is 64.4 inches.

On my road bike, I tend to favor 53-19 (77) or 20 (73.1) on the flats, 39-21 (49.6) or 23 (45.3) on moderate hills.

So . . . which might be the better choice for me? Or am I thinking of this all wrong? What else should I be considering in making my choice?

Building up my first SS which has a 42 tooth chainring. Trying to decide between a 17 or 18 cog. I live in Southern NH, always mildly hilly. I'm 135# and a good climber. Like to spin relatively high cadences.

Used a gear inch calculator; for my setup, 42-17 is 68.2 inches and 42-18 is 64.4 inches.

On my road bike, I tend to favor 53-19 (77) or 20 (73.1) on the flats, 39-21 (49.6) or 23 (45.3) on moderate hills.

So . . . which might be the better choice for me? Or am I thinking of this all wrong? What else should I be considering in making my choice?

Thanks.

I run 42x17 singlespeed in hilly Seattle with 700x32 tires with pretty heavy wheels. It works pretty well for me. If you plan to take the bike off road and/or plan to run huge tires 42x18 would be a better choice.

You have the facts you need, and for a bike to run around town on, and frankly either will be fine. If you like pushing and higher tops speeds a little more then go for the 17, otherwise the 18 is better. Thats about all there is to it. And since this is SS you dont need to worry about skip patches and all that.

I know it may seem like a big decision (I do the same thing when considering bike parts), but just get one and if you end up not liking it after a few months change it up. Its not like it cant be replaced for a relatively small amount of money.

also, why not buy both cogs and try each out? you won't even need to shorter/lenghten the chain when you swap between the cogs.

+1. Buy several cogs. Part of the fun of riding FG/SS is trying to choose the right gear for the ride. 42/17 and 42/18 both seem low to me for the road, but I don't know you or how steep your hills are. If you are a very casual rider, a difference of one tooth may not mean much, but if you really want to hammer along for a good distance, adding or subtracting a tooth can have a notable impact on your overall speed and/or level of exhaustion, and the only way you'll know which gear is best is to experiment with several.

you know what, there isn't really going to be such huge noticeable difference between these two.

also, why not buy both cogs and try each out? you won't even need to shorter/lenghten the chain when you swap between the cogs.

The difference will be noticeable. I'm definitely more comfortable at 42/17 than I was at 42/16. It didn't really change my riding style or my life at all, but it is easier on the hills. Going up 1 tooth in the rear is roughly the equivalent of going down 3 teeth in the front.*

I'll second the idea of buying a few different cogs. Make sure you know the proper way to install/remove the cog and lockring though, because you don't want to strip your hub.

*someone correct me if I have the numbers wrong here. I haven't seen them in awhile.

Originally Posted by Jacquie Phelan

Until mountain biking came along, the bike scene was ruled by a small elite cadre of people who seemed allergic to enthusiasm.

We have very little in common, but I'll submit another data point. I'm an old (50), fat (200#) guy living in the (mostly) flatlands, (but it can be windy) and I like to spin. I'm running 42x17/40x19 SS on my San Jose commuter. Bike has fenders, so flipping is a *****. I have a 17/19 Dos ENO freewheel and 42/40 crankset. The 40/19 is my "once in a great while headwind ride home gear", otherwise I use the 42x17. Nice thing is, when I change gears the chain length isn't affected, so brakes, fenders, etc, don't cause problems.